The present invention claims priority from Japanese Patent Application No. 11 (1999)-243077, which is incorporated by reference herein in its entirety.
The present invention is directed to a motor driving control device. Specifically, the present invention is related to a motor driving control device in which a motor driver is operated to be free from possible heat breakage or destruction while the rotor of the motor rotates at a very low speed or is in locked condition.
For example, in order to drive a switched reluctance motor, hereinafter referred to as an SR motor, a switching module (IPM) is used. The switching module includes a pair of chopping energization circuits, each of which has an insulating gate type bipolar transistor (IGBT), that are provided to a phase coil. Thus, if the SR motor is of three phases, the SR motor has six chopping circuits (2xc3x973) in total, and these chopping circuits are assembled into the switching module (IPM). In the case where the SR motor is mounted on an electrically powered vehicle for driving wheels, the SR motor is energized when the electrically powered vehicle is started and decelerated. Under such conditions, the wheels are rotated at a very slow speed and stopped, and, therefore, the SR motor is rotated at a very slow speed and stopped, respectively. Thus, a motor lock occurs very frequently.
In the locked condition, the electric coil of a specific phase is made to be energized in continuous fashion, which may make the temperature of the IGBT rise above its heat proof temperature or upper temperature limit. Thus, under the possible motor locked conditions, a protection design has to be made in order to prevent the heat breakage (or destruction) or malfunction of the switching module. Of course, for the vehicle to travel, it is also necessary to energize the motor.
The inventors of the present invention have proposed a motor driving control device for the prevention of the heat breakage of a switching module that has been published as Japanese Laid-open Print No. Hei. 10-337084. In this device, while a switching module is being monitored by a temperature sensor, a target current value is adjusted or corrected on the basis of the temperature changing speed that corresponds to the current flowing through the switching element, as a load, of the module. The temperature changing speed becomes higher and lower when the detected current passing through the load is large and small, respectively. The temperature of the individual phase switching element in the switching module is calculated or estimated and, correspondingly, the motor driving current is adjusted.
In this device, the temperature rise inside the switching module is calculated in estimating fashion on the basis of the temperature changing speed (estimated value) that corresponds to the energization current value. This estimation is so rough that the motor fails to output its performance fully, giving priority to the prevention of heat destruction of the switching element. However, in light of the fact that in the motor locked condition a high output torque is required, the current passing through the phase coil has to be as large as possible. According to the inventors"" experiments, while the SR or electric motor is in rotation in steady fashion, the current flowing through the phase coil fails to increase excessively, so that the switching module is not brought into heat destruction. Thus, under motor locked condition, a more strict in-module temperature estimation and as high as possible energization level of phase coil (flowing current through the phase coil) within a range which is free from thermal destruction are desired.
It is, therefore, a principal object of the present invention to provide a motor driving control device in which as high as possible phase coil energization level is achieved while also preventing thermal destruction of the power switching element by using a more precise thermal detection of a portion of a power switching element inside the switching module that is subject to thermal destruction or breakage.
In order to attain the foregoing object, a first aspect of the present invention provides a motor driving control device, including:
a switching module having therein a power switching element for energizing an electric coil of a motor;
energization indication means for providing an energization indication signal to the switching module for energization of the electric coil;
calculation means for calculating a saturation temperature of the switching element generated by the heat generated by an electric loss which results from the continuous energization of the electric coil, the calculation means calculating an inner temperature of the switching element based on the calculated saturation temperature and a time constant xcfx84 of a temperature rise by the generated heat, assuming that the temperature rise is made in first order lag in response to the increase of the heat capacity; and
means for decreasing the current to be applied to the electric coil in accordance with the temperature difference between an upper limit temperature of the power switching element and the calculated inner temperature of the power switching element.
The current to be applied to the electric coil through the energization indication means is decreased when the temperature difference is equal to or below a predetermined value, the current decrease becoming bigger as the temperature difference becomes smaller.
The heat generation inside the module generates at a junction in the switching element, and, therefore, thermal destruction occurs thereat. The electric power consumed at the junction or electric power loss (Lt) depends on the specification of the power switching element and amounts of energizing current and voltage and, therefore, can be calculated precisely according to the specification of power switching element. When the heat generated by the electric power loss (Lt) is converted into a temperature according to the thermal resistance of the element, such a temperature is a saturation temperature which can be attained when the energization is continued and is calculated in relatively precise fashion. The junction temperature Tjnow of the power switching element can be obtained on the basis of the saturation temperature and a time constant xcfx84 of a temperature rise by the generated heat subject to that the temperature rise is made in first order lag fashion relative to the increasing heat amount. These calculations or estimations are high in precision and, therefore, the value of the obtained junction temperature (Tjnow) is very reliable.
On the other hand, the upper temperature limit (Tjmax) of the switching element is provided together with the module by the manufacturer thereof and is highly reliable. If the difference, Error (Error=Tjmaxxe2x88x92Tjnow), between the detected inner temperature (Tjnow) and the upper temperature limit (Tjmax) becomes equal to or less than a predetermined value (K3), the decreasing degree of the current flowing through the electric coil becomes greater as the difference becomes smaller, so that the thermal destruction of the power switching element can be prevented. In addition, the junction temperature (Tjnow) is kept below or less than the upper temperature limit (Tjmax), and a relatively high current can be made to flow through the electric coil producing as high as possible torque.
A second aspect of the present invention is to add, to the device according to the first aspect, detection means (1d, 11) for detecting a rotation number (or speed) of the motor (1). Such a driving control device operates as follows: the means (11) for calculating the electric power loss (Lt) and the means for calculating the junction temperature (Tjnow) make calculations only when the motor rotation number is less than the motor lock judging threshold value (e.g., 10 rpm). The current decreasing means (11) decreases the current only when the motor rotation number is less than the motor lock judging threshold value (e.g., 10 rpm).
When the motor is not in its locked condition, a large output torque is not required, which results in that the target current value is low and the motor current fails to become excessive, so that no current flows through the switching element inside the module that increases the junction temperature over the upper temperature limit (Tjmax). Thus, the normally operated switching element is free from thermal destruction, which means that detecting the junction temperature (Tjnow) is unnecessary. Thus, in light of such circumstances, the foregoing three means are made to be at rest for reducing the respective jobs.
A third aspect of the present invention is to operate the current decreasing means (11) for decreasing current under proportional control (step 90 in FIG. 3 and steps 65 and 66 in FIG. 2) which is based on the difference (Error=Tjmaxxe2x88x92Tjnow) between the junction temperature (Tjnow) and the upper temperature limit (Tjmax). According to this aspect, whenever there is a motor locked condition, the junction temperature (Tjnow) is kept automatically below or less than the upper temperature limit (Tjmax) and a relatively high current can be caused to flow through the electric coil to produce as high as possible torque. Thus, ideal motor driving can be realized even when the motor is in its locked condition.